Photoresist compositions are used in microlithography processes for making miniaturized electronic components such as in the fabrication of computer chips and integrated circuits. Generally, in these processes, a thin coating of film of a photoresist composition is first applied to a substrate material, such as silicon based wafers used for making integrated circuits. The coated substrate is then baked to evaporate any solvent in the photoresist composition and to fix the coating onto the substrate. The baked coated surface of the substrate is next subjected to an image-wise exposure to radiation.
This radiation exposure causes a chemical transformation in the exposed areas of the coated surface. Visible light ultraviolet (UV) light, electron beam and X-ray radiant energy are radiation types commonly used today in microlithographic processes. After this image-wise exposure, the coated substrate is treated with a developer solution to dissolve and remove either the radiation-exposed or the unexposed areas of the photoresist.
The trend towards the miniaturization of semiconductor devices has led to the use of new photoresists that are sensitive to lower and lower wavelengths of radiation and has also led to the use of sophisticated multilevel systems to overcome difficulties associated with such miniaturization.
Absorbing antireflective coatings and underlayers in photolithography are used to diminish problems that result from back reflection of light from highly reflective substrates and to provide better masking properties during dry etching. An antireflective coating coated beneath a photoresist and above a reflective substrate provides significant improvement in lithographic performance of the photoresist. Typically, the bottom antireflective coating(s)/underlayer(s) are applied on the substrate and then a layer of photoresist is applied on top of the antireflective coating. The antireflective coatings are cured to prevent intermixing between the antireflective coatings and also between the top antireflective coating and the photoresist. The photoresist is exposed imagewise and developed. The antireflective coating in the exposed area is then typically dry etched using various etching gases, and the photoresist pattern is thus transferred to the substrate. Multiple antireflective layers and underlayers are being used in new lithographic techniques. In cases where the photoresist does not provide sufficient dry etch resistance, underlayer is or antireflective coatings for the photoresist that act as a hard mask and are highly etch resistant during substrate etching are preferred, and one approach has been to incorporate silicon into a layer beneath the organic photoresist layer. Additionally, another high carbon content antireflective or mask layer is added beneath the silicon antireflective layer, which is used to improve the lithographic performance of the imaging process. The silicon layer may be spin coatable or deposited by chemical vapor deposition. Silicon is highly etch resistant in processes where O2 etching is used, and by providing a organic mask layer with high carbon content beneath the silicon antireflective layer, a very large aspect ratio can be obtained in the substrate pattern. Thus, the organic high carbon mask layer can be much thicker than the photoresist or silicon layer above it. The organic mask layer can be used as a thicker film and can provide better substrate etch masking that the original photoresist. Thus there is a need for better antireflective layers and underlayers which provide superior lithographic properties, especially those with high carbon content.